Regenerated collagen fibers are generally manufactured, using hides and bones obtained from slaughtered animals as a raw material, telopeptides of collagen is decomposed and obtained the water soluble collagen by treating the materials with alkali or enzyme treatment, and then the obtained soluble collagen is spun into fibers. The spun fiber is then given various treatments according to usage. For example, performed is a treatment of combination of two methods using mono functional epoxy compounds and aluminum salts to the collagen (WO02/52099), and after the treatment, drying process is given in order to remove water included in the fiber.
Regenerated collagen fibers have properties of: having a very small tensile strength of fiber containing water before drying; giving easy occurrence of yarn breakage (fluff) under drying; showing shrinkage in drying but no stretch-ability; giving yarn breakage by compulsory stretching; and showing large unevenness in shrinking behavior according to drying conditions. Furthermore, there are problems that an excessively reduced tension under drying for fear of yarn breakage increases shrinkage of the regenerated collagen fiber under drying, and further fails to retain the curl retentive property as one of important quality of head decorating fibers at termination of drying, impairing commercial value thereof.
As drying conditions in batch methods, a drying method of regenerated collagen fibers is indicated by WO02/52099, wherein drying is preferably performed under conditions of drying temperatures of not more than 100 degree C. and more preferably not more than 75 more degree C. and a load of 0.01 to 0.25 g weight per 1 dtex, and preferably 0.02 to 0.15 g weight.
From the viewpoint of improving productivity, development of a continuous drying method and a device therefor is necessary, but there are problems of occurrence of fluff (yarn breakage) and tension control of a fiber running in a dryer etc., and therefore continuous drying of a regenerated collagen fiber is not yet in a situation of practical use.
In manufacturing of general synthetic fibers such as acrylic and polyamide fiber, these fibers differ from regenerated collagen fibers and thus allow stretching under drying and heat treatment. Therefore, under existing circumstances, general-purpose dryers of hot-air drying system using a plurality of driven rollers or heat rollers system may be used, and rotational speeds of the driven rollers are gradually increased in areas closer to an exit of the process, to dry the fibers accompanied with concurrent stretching in order to prevent hang-down of the fiber bundles in processes after drying including drying stage, or in order to adjust denier value (thickness) of a fiber, or in order to improve quality, such as strength. In contrast, regenerated collagen fibers can not allow stretching under drying, and compulsory stretching forms break of fiber bundles and causes resultant process trouble. Furthermore continuous drying without stretching makes the fiber bundles under drying give drying unevenness, forms difference in the shrinkage length in the fiber bundle, and forms resulting fiber bundle hang-down in a following drying step, thus leading to wound around rollers of the hung down bundle, and to slipping of the fiber out of the rollers. As a result, these disadvantages cause fiber breakage or breaking of the fiber bundle, and lead to situation of operation failure.
On the other hand, some prior art references indicate methods of continuous drying and apparatus using a fixed tension. For example, Japanese Patent Laid-Open No. 48-22710 gazette indicates an apparatus having a plurality of dryers for maintaining a low tension, and a plurality of driven rollers (yarn feeders) intervened therebetween, for the purpose of improvement in dimensional stability of cuprammonium rayon fibers.
However, adoption of this apparatus in drying of regenerated collagen fibers makes difficult maintenance of a fixed fiber tension between each of the driven rollers. The difficulties are attributed to the fact that drying shrinkage takes place immediately after the fibers come into falling rate drying region in drying of regenerated collagen fibers, and a change of drying conditions greatly varies shrinking behavior of the fibers, and makes difficult determination of a specified position of shrinkage of the fiber within the dryer, therefore shifting the shrinking position within the dryer. Accordingly, control of shrinking behavior of the fibers is very difficult to be adjust to a reduction ratio of the driven rollers, that is sections having a higher fiber tension and a lower one may be formed, a section having a higher fiber tension gives fiber breakage (fluff), and a section having a lower section gives fiber hang-down, leading to process trouble.
A document indicates a method using a plurality of Nelson rollers or tapered rollers with a fixed tension for drying, aiming at manufacturing a high modulus type PPTA fiber having few fluffs (Japanese Patent Laid-Open No. 60-88117 gazette). In the case where this apparatus is adopted for drying of regenerated collagen fibers, however, the above-described disadvantages make difficult adjustment of a tapered angle of the Nelson rollers or the tapered rollers with respect to shrinking behavior of the fibers, and therefore a section having a higher fiber tension gives fiber breakage (fluff), and a section having a lower section gives fiber hang-down.
Furthermore, a document indicates a manufacturing method of aiming at drying a high modulus fiber with outstanding abrasion-resistance under a fixed tension, wherein the fiber is passed on a heated roller (heat roller) and between rollers (Japanese Patent Laid-Open No. 04-214434 gazette). However, when these heat rollers used in drying regenerated collagen fibers, a usual straight drum type heat roller makes the fiber continuously shrink and raise a tension thereof as drying advances. As a result, control of tension becomes uncontrollable, leading to inevitable breaking of the fiber bundle (tow). Therefore, in the case of regenerated collagen fibers, use of the heat roller alone in continuous drying operation may not be adopted.
In addition, a certain method is found out that drying can be performed by controlling a rotational speed of a yarn guide roller and thus by controlling a stretching tension, aiming at manufacturing of a hollow fiber for cellulosic blood treatment having characteristic showing slight shrink in wet condition (Japanese Patent Laid-Open No. 57-14359 gazette). This apparatus is characterized by a structure of having a driven roller (yarn guide roller and taking up roller) currently installed in an entrance of the dryer, and also of a drying system of one pass having no rollers within the dryer. Here, in drying of regenerated collagen fibers, needed is at least 90 m for a residence length of the dryer calculated from viewpoints of operating condition (drying time not less than 30 minute) in consideration of quality and productivity (processing speed not less than 3 m/minute).
Accordingly, realization of a dryer having one pass of not less than 90 m either by horizontal or vertical type is very difficult, in consideration of conditions for installation construction cost, operability, etc., and therefore adoption a single passage dryer having no rollers within the dryer in drying for regenerated collagen fibers may not be practical.
As previously described, in manufacturing of head decorating regenerated collagen fibers, there have not yet been found out methods and apparatus enabling continuous drying, without any process trouble, of the regenerated collagen fibers having outstanding quality.